Mass transport in soft biomaterials can be imagined as particle or molecule movement through a matrix there the surrounding structure acts as a sieve. Diffusion and flow are the two major mass transport mechanisms in soft biomaterials. Diffusion is random motion driven by the internal heat of the system. Flow is a coherent motion of fluid volumes driven by external forces. Diffusion and flow are influenced by obstruction, interactions, structure dynamics and the properties of the liquid phase. For instance, the structure prolongs the diffusion path or gives rise to large pressure drops for flow depending of the length scale. Depending on e.g. external pressure, particle diffusion constant and biomaterial structure, diffusion and flow may compete for being the dominating mass transport mechanism, which typically occurs at length scales of approximately 100 – 200 nanometers in the biomaterials of interest to SuMo. Furthermore, the structure of many of the SuMo biomaterials are heterogeneous, and/or hierarchical with length scales ranging from a few nanometers up to several micrometers, which influences the mass transport at both local and global scale. Properties of the diffusing particle such as size, shape, charge, hydrophobicity or fluid properties such as viscosity and it’s interplay with the surrounding structure is also of vast importance for the mass transport. Electrostatic interactions are important because positive attraction can lead to binding and retard molecular movement and negative interactions can lead to smaller effective volumes accessible for transport. Having access to experimental techniques for characterizing the relative contributions from diffusion and flow, interactions between diffusing particle or fluid as well as particle or fluid properties are essential for the development of new biomaterials with tailored mass transport properties.
In this module the overall research question is related to how the diffusion and/or flow rates depend on the structure of the material, i.e. mass transport – microstructure relationships. For this purpose we use several different experimental techniques for diffusion and flow characterization at different length –and time scales and determination of the effect of electrostatic interactions. Since the structure of a biomaterial may vary greatly depending on its origin so can diffusion and flow. In very crowded structures the mass transport may be very slow making diffusion the dominating mechanisms. In materials with larger structures, such as a cellulose fiber material, the flow mechanism may dominate. This module in combination with module 2 serves as experimental input to module 3: where the results will be used for validation of mass transport modeling and inspiration for development of new simulation techniques. Module 4 will provide interesting materials in which the diffusion and flow techniques can be applied.